1. Field of the Invention
The present invention relates to lasers and particularly to a diode-pumped, fiber laser doped with thulium activator ions for producing an output CW laser emission at a wavelength of substantially 2.3 microns.
2. Description of the Prior Art
In low power applications, such as in telecommunications and in medical and sensing applications, the use of fiber lasers is becoming more and more important.
In a typical fiber laser a rare earth, such as erbium, neodymium, terbium or praseodymium, is doped into the core of an optical fiber to provide an active gain medium for the fiber laser. Typically, the optical fiber is comprised of silica. The input end of the fiber laser is pumped with optical radiation to produce lasing action in the fiber laser at a wavelength essentially determined by the dopant and the mirror reflectivities. The doped optical fiber is included in the laser resonant cavity of the fiber laser.
A major disadvantage of using a silica fiber as the host optical fiber for the dopant rare earth is that a silica fiber is not suitable for transmitting wavelengths longer than 2 microns. The reason for this is that there is too much attenuation of light in the silica fiber at wavelengths above 2 microns.
Intense research and development have been conducted in the area of fluorozirconate (ZrBaLaNa or ZBLAN) glasses to produce ultra-low-loss fibers for optical communications. Minimum transmission losses in ZBLAN fibers occur over the wavelength range between 2 and 3 microns. It is, therefore, highly desirable to develop ZBLAN rare earth fiber lasers in this wavelength range.
The first demonstration of a 2.3 micron, thulium-doped, ZBLAN fiber laser was demonstrated by Leon Esterowitz and Roger Allen, the inventors in the present application. Pulsed operation was achieved by pumping with a pulsed alexandrite laser. The work was presented at the Lasers '87 Conference in December 1987, at the IEEE/LEO's '88 Annual Conference in November 1988 and at the Conference on Lasers and Electro-Optics in April 1988, and was published in "Electronics Letters", Vol. 24, No. 17, pp. 1104-1106, Aug. 18, 1988. The fiber laser did not operate in the continuous wave mode and was inconveniently pumped by a large alexandrite laser.